a) Field of the Invention
The invention is directed to a device for flat illumination of an object field in an optical instrument and to an optical instrument with a device of this kind. Optical instruments of this type are, for example, microscopes, including microlithography simulation microscopes in which a flat illumination, i.e., illumination extending beyond a singular object point, of the object to be examined is required.
b) Description of the Related Art
In instruments of the type mentioned above, the homogeneity of the illumination of the object field is particularly important as regards the quality of the recorded images of the object field. To this extent, the problem with using laser light sources for generating the illumination light is that the intensity of the light is unevenly distributed within the beam cross section, which has a disadvantageous effect on image quality.
Other variations in the brightness of the illumination which disadvantageously affect the image quality and, therefore, the results of evaluation are caused by low-frequency amplitude modulations or coherent noise (speckle) in coherent light sources. Therefore, an important concern consists in reducing these interfering influences as far as possible.
For this purpose, in a solution which is already known, a rotating diffusion screen or scatter disk is arranged in the beam path between the laser light source and the object field in order to reduce the intensity modulation of the laser light.
Further, it is known to use light-conducting cable in connection with optical instruments. These light-conducting cables have been used heretofore to transmit light from the source to the object in the most flexible manner possible. Usually, the light-conducting cable is used to transfer illumination light within the spectral range from longwave (λ>400 nm) to infrared.